High-Q Microring Resonators With 2 x 2 Angled Multimode Interference Couplers

High Q-factor microring resonators (MRRs) with 2 x 2 angled multimode interference (MMI) couplers are realized based on SU-8 polymer strip waveguides, which has an SU-8 polymer core, an SiO2 buffer, and an air cladding. The present MRR has a small radius (150 mu m) because of the high-index contrast of the SU-8 optical waveguides. The coupling ratio of the angled MMI couplers is adjusted to achieve a high-loaded Q-factor MRR by modifying the bending angle. When this bending angle is chosen as 3.25 degrees, the Q-factor of the fabricated MRR is about 25 000.